8.3.4 Libtool Libraries with Conditional Sources

Conditional compilation of sources in a library can be achieved in the
same way as conditional compilation of sources in a program
(see Conditional Sources). The only difference is that
_LIBADD should be used instead of _LDADD and that it
should mention libtool objects (.lo files).

So, to mimic the hello example from Conditional Sources,
we could build a libhello.la library using either
hello-linux.c or hello-generic.c with the following
Makefile.am.